I also have the Metrolux II. Since it does not measure seconds but lux units, or units of light, then I don't think that 3x10 or 30 seconds would be any different.

Fred Pickers unit was a Zone VI and it also was a lux unit and thats why I don't think he had any differences with the 3x10 vs 30 either.

Where the differences come into play, in my opinion is bulb warm up in the timers that measure strickly seconds.

Michael McBlane